Uncategorized
Vernal Pools
Feb
Above: Vernal pool at Greenbrier Park. Photo by Emily Luebke, PDC
By Emily Luebke, Senior Field Technician and Photographer
CLASSIFICATION: What’s in a name?
Vernal means “of spring”—appropriate since spring is when these pools are generally most full of water and life! Other names, including seasonal pool, spring pool, temporary pond, and ephemeral pool, make references to the fact that these pools do not always contain water. Another name, woodland pond, gives a hint as to where some of these pools may be found.1,2
Vernal pools are wetlands that vary widely in terms of their surrounding plant communities, animal communities, water sources (runoff, groundwater, snowmelt, rainfall), and the period of time in which the pool contains water.1,2
Broadly defined, vernal pools all share several characteristics:1,2
- Small size and shallow depth
- Not permanently connected to other bodies of water
- Typically will dry out annually in summer or fall, though may only get very low each year and dry out occasionally
- Support species that are adapted to and dependent on this seasonal drying, which precludes fish populations from permanently establishing
The very characteristics that define vernal pools, plus the fact that many do not meet criteria to be classified as wetlands that have state or federal protection (often because they are isolated and small), mean that these important habitats are at risk from human impacts. As a result, vernal pools have likely been lost at a similar or higher rate than larger wetlands.1 A recent study concluded that the U.S. has lost more than half of all its wetlands, and the rate of loss is currently increasing despite recognition of the important services they provide for humans (mitigating severe storms, sea level rise, and flooding to name a few) and animals (about half of endangered species in the U.S. depend on wetlands)!4
These special places need our help and protection!
LOCATION: Where do you find them?
Vernal pools may be found across the state and the country. While they vary remarkably, they may be organized by the landscapes that surround them: upland, wetland, or floodplain. When surrounded by upland, the pools may appear as scattered oases with water and food within the upland forest. When located within a wetland, the pools are part of a larger wetland complex. Pools in a floodplain of a river or stream may have temporary connections to the river or stream during flooding events.4 What kind of landscape surrounds you here?
A few of the more unusual types of vernal pools are found in Virginia and the mid-Atlantic. Sinkhole ponds found from Augusta to Page counties are formed when the underlying limestone dissolves. Low spots on gentle uplands with hard clay soils that impede drainage host vernal pools known as upland depression swamps. Portions of the Delmarva Peninsula have thousands of vernal pools known as Delmarva bays, a name derived from the many bay trees growing there. What kind of landscapes have vernal pools where you live?
CONNECTIONS: What are its relationships to other plants, animals, and humans?
Flora associations: The specific species of plants associated with a vernal pool can vary depending on the surrounding landscape, but they will be species that tolerate wet to flooded conditions. These may include trees such as red maple (Acer rubrum), black gum (Nyssa sylvatica), willow oak (Quercus phellos), willows (Salix spp.), pin oak (Quercus palustris), American holly (Ilex opaca), and American elm (Ulmus americana). Shrubs and herbaceous vegetation could include buttonbush (Cephalanthus occidentalis), smooth alder (Alnus serrulata), rice cutgrass (Leersia oryzoides), sedges (Carex spp.), and woolgrass (Scirpus cyperinus).1
Virginia sneezeweed (Helenium virginicum), a federal and state-listed threatened species, grows only in 30 sinkhole ponds in Virginia and 30 ponds in Missouri! There is much left to learn about plant species restricted to these special habitats!5
Fauna associations: Vernal pools provide important habitat for a wide variety of fauna. They provide critical breeding habitat for many amphibians, some of which only reproduce in vernal pools. Many of these amphibians are rare, threatened, or endangered, as are some of the numerous invertebrates that live in vernal pools. All these living creatures are also a food supply for other animals, making vernal pools a critical part of food webs.1,2
The area encompassing a vernal pool is often thought of as having three zones: the pool depression (all areas inundated when water is at its highest level), the pool envelope (area up to 100 ft. from the pool), and the terrestrial habitat (area up to 1,000 ft. from the pool). All these zones serve different functions. As pool depressions fill with water throughout the late winter and early spring, they come to life! On warm, wet nights, wood frogs and spring peepers begin calling, amphibians migrate to the pools to breed, and numerous invertebrates in the pools become active. Many other animals, such as owls, raccoons, and snakes, make their way to the pools to feast on breeding amphibians and their eggs! During the breeding season (late winter and spring), many adult amphibians may be found in the pool envelope, while young amphibians beginning life on land stay close to the pool as they continue to develop. When they mature, they migrate into the terrestrial habitat where they spend roughly 90% of their lives.1
Fauna of vernal pools are often classified as either indicator species or facultative species. Indicator (or obligate) species have evolved to depend on vernal pools for completing their life cycles. Indicator species for vernal pools in Virginia include six species in the mole salamander family (Ambystoma spp.), wood frog (Lithobates sylvaticus), eastern spadefoot (Scaphiopus holbrookii), and some fairy shrimp (Eubranchipus spp., Streptocephalus sealii). Facultative species use vernal pools (possibly for breeding, food, water, or cover), but they do not require a vernal pool for reproduction and successful completion of their life cycles. Vernal pools have lots of facultative species, including other amphibians, snakes, turtles, mammals, birds, and many aquatic invertebrates.1,2
To visit our separate page for each of these indicator species and learn more, click on each photo below!
Additional Indicator Species: In Virginia, there are four other salamanders of the genus Ambystoma—the state threatened Mabee’s salamander (Ambystoma mabeei), the state endangered eastern tiger salamander (Ambystoma tigrinum), the Jefferson salamander (Ambystoma jeffersonianum), and the mole salamander (Ambystoma talpoideum). The eastern spadefoot (Scaphiopus holbrookii) and fairy shrimp (Eubranchipus spp., Streptocephalus sealii) also depend on vernal pools.1,2
Fun Fact: In order to hatch, the eggs of the fairy shrimp must first dry out before again being submerged. The eggs can remain dry for years, and even survive if ingested by animals, but when the conditions are right in the vernal pool they will hatch!1,2
Additional Facultative Species: Many other frogs and toads can be observed at vernal pools, including green frogs (Lithobates clamitans) and Northern cricket frogs (Acris crepitans). Numerous types of invertebrates live in the pools—clam and seed shrimp, isopods, amphipods, predaceous diving beetles, mosquito larvae, caddisfly larvae, and water mites to name just a few! During the spring, spotted turtles (Clemmys guttata) depend on vernal pools as a valuable source of food—they like the invertebrates and amphibian eggs!1,2,3
Other species come to the vernal pools to feed on invertebrates, amphibians, and amphibian eggs, or drink water. Some of these species include snakes (such as northern water snakes, eastern garter snakes, and ribbon snakes), turtles (such as eastern box turtles), birds (such as owls, herons, and wood ducks), and mammals (such as raccoons, bats, and more).1,2,3
Human associations: Human activity is responsible for the loss or degradation of many vernal pools. Pools may be filled so the land can be used for development, agriculture, or forestry. Since some amphibians (like spotted salamanders) return to the same pool each year to breed, the loss of their pool may mean they fail to successfully reproduce again. Even development that does not appear to directly affect a vernal pool may have unforeseen negative effects. Remember that spotted salamanders spend 90% of their lives in the upland forests up to 1,000 ft. away from the pools! This habitat is critical for their survival, but may be turned into homes, lawns, etc. Development may also change the water levels, water chemistry, water temperature, and amount of sediment in nearby vernal pools.
Why is this salamander (right) crossing the road?
It needs to get from the upland forest where it lives across the road to the vernal pools where it will breed! Roads (and the cars driving on them) pose an immediate hazard for migrating salamanders, and may also increase run-off, trash, and chemical pollution at the pools.1,2 There are a lot of threats to the survival of the amazing creatures that depend on vernal pools!
As the importance of vernal pools and the impacts humans have on them become more apparent, many scientists, state organizations, and other groups have stepped in to locate and monitor vernal pools. Some localities build wildlife tunnels or close roads on migration nights so the salamanders can cross safely! Despite these efforts, more research and protection is needed to better understand and preserve these special places.1,2 Locally, Piedmont Discovery Center has devoted more than a decade to documenting and bringing attention to the salamander populations living and breeding near Polo Grounds Rd. and Rio Mills Rd. in Albemarle County (read more here). After many years leading volunteer efforts to help salamanders safely across the road, PDC advocated for the installation of salamander tunnels under Polo Grounds Rd. to provide safe passage during migration. The result was a collaborative effort among many groups in the community towards the completion of the salamander tunnels in 2020 (read more here). PDC continues to educate the community about vernal pools and animals connected to them through public events at Rio Mills Rd. and the adjacent Brook Hill River Park. To learn more about this important ongoing work, watch this YouTube documentary and this episode of PBS “Untamed”.
IDENTIFICATION: What does it look like?
Vernal pools are often overlooked—maybe just thought of as a place that is wet part of the year—and not recognized as the important habitats they truly are!
Do you think you might have found a vernal pool? To know for sure, you need to make a number of observations:1,2
Is it relatively small and shallow? A survey of vernal pools in the Mid-Atlantic showed that the vast majority are less than 0.1 acre (about 4,300 sq. ft. or 400 sq. m.) and have a maximum depth of less than 15.7 inches.1
Have you checked to make sure there are no lasting connections between this pool and any rivers, creeks, or other permanent bodies of water? Keep in mind this might mean checking at different times of year as flooding may cause temporary connections.
Does the pool dry out during the year? If not, does it dry out at least periodically during droughts? These drying events are important as they preclude fish from permanently inhabiting the pool. Again, get familiar with the pool by checking at different times of year and looking for fish!
Do you see any indicator species—those that are dependent on these fish-free environments for successful reproduction? Remember that, in our area, those include six species in the mole salamander family (Ambystoma spp.), wood frog (Lithobates sylvaticus), eastern spadefoot (Scaphiopus holbrookii), and some fairy shrimp (Eubranchipus spp., Streptocephalus sealii).
If you answered YES to all the above questions, you have found a vernal pool! We want these pools to continue to provide valuable habitat for the creatures dependent on them to thrive, and for everyone who gets to visit the park to enjoy them, so remember—don’t litter, don’t disturb the wildlife, and don’t go wading through the pools!!
Bibliography & Definitions
1 Brown, L.J. and R.E. Jung. 2005. An Introduction to Mid-Atlantic Seasonal Pool, EPA/903/B-05/001. U.S. Environmental Protection Agency, Mid-Atlantic Integrated Assessment, Ft. Meade, Maryland.
2 Kenney, Leo P, and Matthew R. Burne. A Field Guide to the Animals of Vernal Pools. 2000. Third printing ed., Massachusetts Division of Fisheries & Wildlife Natural Heritage & Endangered Species Program & Vernal Pool Association, May 2009.
3 Kleopfer, J.D., J.C. Mitchell, P.W. Sattler, and S.H. Watson. 2020. A Guide to the Salamanders of Virginia. Special Publication Number 7, Virginia Department of Game & Inland Fisheries. Richmond, VA. 76 pp.
4 Lang, M.W., Ingebritsen, J.C., Griffin, R.K. 2024. Status and Trends of Wetlands in the Conterminous United States 2009 to 2019. U.S. Department of the Interior; Fish and Wildlife Service, Washington, D.C. 43 pp.
5 “Digital Atlas of the Virginia Flora | Helenium Virginicum Blake.” Vaplantatlas.org, 2025, www.vaplantatlas.org/index.php?do=plant&plant=2129&search=Search. Accessed 16 Jan. 2025.
Definitions:
Indicator species: A species that is dependent on vernal pools to successfully reproduce and complete its life cycle.
Facultative species: A species which uses vernal pools (possibly for breeding, food, water, or cover) but that does not require a vernal pool for reproduction and successful completion of its life cycle.
